A conventional mono-tube shock absorber comprises a cylinder defining a working chamber having a piston slidably engaging the cylinder within the working chamber. The piston divides the working chamber into an upper working chamber and a lower working chamber. A piston rod is connected to the piston and the piston rod extends through the upper working chamber and through one end of the cylinder. An extension valving system is incorporated into the piston for generating a damping force during an extension stroke of the shock absorber and a compression valving system is incorporated into the piston for generating a damping force during a compression stroke of the shock absorber. In a dual tube shock absorber, a reservoir tube surrounds the pressure tube to define a reservoir chamber. A base valve assembly controls fluid flow between the working chamber and the reservoir chamber. An extension valving system is incorporated into the piston for generating a damping force during an extension stroke of the shock absorber and a compression valving system is incorporated into the base valve assembly for generating a damping force during a compression stroke of the shock absorber. The piston includes a compression valving system to regulate the pressure drop across the piston during the compression stroke and the base valve assembly includes an extension valving system to regulate the pressure drop across the base valve system during the extension stroke.
In some applications, the shock absorber is required to limit the full extension travel of the vehicle's suspension system. When the shock absorber is used as an extension stop for the vehicle's suspension system, it is important to provide some type of mechanism or system which provides a cushion for this stop to avoid the excessive loading and/or noise which occurs when there is a metal to metal stop. Built into the shock absorber, one typical extension stop is a resilient bumper made of some type of elastomeric material. The bumper is designed to cushion the impact between the piston and the top of the pressure tube. While these types of extension stops help to cushion the impact, they still provide an abrupt means for limiting the travel and the elastomeric material may experience heat degradation which reduces its ability to limit the impact.
Another type of extension stop that has been developed is to provide additional hydraulic damping force acting against the piston during the extension stroke when the piston approaches the end of the pressure tube. These systems are known as “hydraulic extension cut-off” or “stop” and they have been effective at cushioning the impact between the piston and the end of the shock absorber.
While the prior art hydraulic extension cut-off designs have been effective at reducing both the loads and the noise associated with the impact between the piston and the end of the pressure tube, the costs and complexities of these designs is excessive and easier and less costly designs or systems are needed which can provide the same and/or additional features.